Modern high-speed data bus standards, such as USB 3.0, DisplayPort, mini DisplayPort, HDMI, and etc., are using copper wires as the data transmission medium. It is beneficial to replace copper wires with optical fibers for the following advantages:    1. Supporting longer transmission distances with less signal attenuation than copper wires;    2. Supporting higher data rate;    3. Reducing jitter due to unmatched wire lengths in the differential pair;    4. Reducing EMI issues due to unmatched impedances;    5. Cheaper cable material costs;    6. Reducing the cable size.
In order to initiate a data transmission, the first data node attached to one end of the cable must actively detect plug-in of the second data node at the opposite end of the cable. This detection process is sometimes also used to identify the type of the node (host, device, hub, and etc.) connected to the cable ends. In a conventional implementation through copper media, the plug-in detection is accomplished through detection of changes of certain electrical properties across copper wires in the cable.
FIG. 1 illustrates two data nodes being connected by a copper cable in a conventional implementation. Referring to FIG. 1, when the cable plugs into the first node 1, the detection circuitry 11 within node 1 monitors the electrical properties across designated copper wires in the cable. When the second node 2 is connected to the cable, its identity circuitry 22 is also connected to the designated wires thus changing the electrical properties across the wires. The properties can be exhibited in the forms of voltage, resistance, current or any other measurable electrical characteristics. FIG. 2 illustrates the copper cable plug-in detection mechanism.
When the copper wires are replaced by optical fibers, an optical-to-electrical converter is required to convert the electrical signal to optical signal for transmission. The optical signal at the receiving end is converted back to electrical signal by an electrical-to-optical converter. Because of this electrical-optical-electrical conversion, the electrical property change induced by plug-in can no longer be detected across the cable thus breaking the plug-in detection protocol. FIG. 3 illustrates a conventional active optical cable (AOC) without the plug-in detection capability. FIG. 4A illustrates a general AOC structure. FIG. 4B illustrates a general AOC structure with power lines and ground lines.